Heterogeneous networks (HetNets) are an attractive means of expanding mobile network capacity. An HetNet may include multiple radio access technologies (RATs), architectures, transmission solutions, and base stations of varying transmission power. HetNets may be able to improve system capacity and user throughput. Some HetNets include macro-cells that are served by macro base stations, such as macro evolved node Bs (eNBs), and smaller cells, such as pico cells, that may be served by pico base stations (pico eNBs),
One issue with these HetNets is providing seamless connections and robust mobility for user equipment (UE) particularly for transitions between macro and small cells. A small cell may be served by lowed power nodes like RRH (Remote Radio Head), Pico eNBs, HeNBs and Relay nodes, In co-channel HetNet deployment a UE may suffer interference when it is located in the cell-edge district. On the other hand, the Reference Signal Receiving Power (RSRP) from a pico cell varies more quickly compared with that from a macro cell. As a result, when a UE is moving towards or leaving pico cell, it may suffer a higher radio link failure (RLF) and/or a handover failure (HOF) before it hands over to a target cell. This is especially an issue for UEs that are moving at a medium or high speed (i.e., traveling in a car). Frequent handover for medium or high speed UEs results in excess overhead large overhead for both eNBs and UEs. Thus how to enhance the mobility robustness in HetNets becomes an open question in reality.
Thus there are general needs for HetNets with improved capacity and user throughput. There are general needs for HetNets that provide enhanced mobility robustness for UEs. There are also general needs for networks that address UE attachment to pico cells.